The present invention relates to a polyamideimide resin for flexible printed circuit boards; a metal-clad laminate, a coverlay, and a flexible printed circuit board that employ this resin; and a resin composition that contains this resin.
Coverlays and flexible printed circuit boards (FPCs), for example, metal-clad laminates, comprising suitable combinations of, for example, an electrically insulating resin layer, e.g., of polyimide film or polyamide film, an adhesive layer in which the main component is epoxy resin or polyimide resin, and an electroconductive metal foil layer, e.g., of copper foil, silver foil, or aluminum foil, are already in use.
FPCs have been made lighter and thinner in recent years accompanying the trend toward lighter and thinner electronic and electric devices.
For example, metal-clad laminates are undergoing a conversion from three-layer substrate structures comprising a resin film layer, adhesive layer, and metal foil layer, to two-layer substrate structures comprising a resin film layer and a metal foil layer.
In the case of coverlays, on the other hand, there are limits on the pursuit of weight and thickness reductions while still maintaining the properties since coverlays comprise only a resin layer and an adhesive layer.
With regard to methods for solving the aforementioned problem of making coverlays lighter and thinner, for example, a printed circuit board is known in which a resin composition layer comprising polyamideimide resin and/or polyimide resin is laminated without an interposed adhesive layer on a metal foil layer that has already been formed into circuitry (for example, Japanese Patent Application Laid-open No. H3-253340).
It is also known that a polyamideimide paint obtained by the reaction of trimellitic anhydride and aliphatic dicarboxylic acid (molar ratio=1:2 to 2:1) with a diisocyanate compound in an amount approximately equimolar with these two components can be utilized as a dielectric layer for dielectric wires (for example, Japanese Patent Application Laid-open No. H7-37438).
Moreover, it is known that a polyamideimide resin composition containing repeat units from naphthalenediisocyanate and, for example, monoanhydride, dianhydride, or dicarboxylic acid, at respective specific molar ratios can be used in metal-clad laminates (for example, Japanese Patent Application Laid-open No. 2005-325329).